Pen-type injectors are regularly used by persons who do not have formal medical training. Accordingly, the application comes along with circumstances that set a number of requirements for drug delivery devices of this kind. In case of improper use such as unintended disassembly actions there is the risk of malfunction and contamination of the medicament stored in the cartridge. Also mechanical parts of the device could be damaged. Therefore, the device must be robust in construction in order to prevent manipulation of the components. Especially with regard to the cartridge holder, which is connected to the housing of the drug delivery device, there is demand for a reliable connection easy to manufacture and to assemble but also safe regarding to any kind of manipulation or malfunction.
The main function of a cartridge holder is to encase and fix a cartridge or an ampoule to the mechanical components of a drug delivery device such that a medicinal product contained within the cartridge can be expelled by e.g. forwarding a piston. A cartridge holder may either be permanently attached to the drug delivery device such that the drug delivery device has to be discarded if the cartridge is empty or the drug delivery device is a reusable device which allows detaching the cartridge holder to replace an empty cartridge by a new one. In the latter case it is inevitable to ensure that the cartridge holder is fully and firmly attached to the drug delivery device after replacing an empty cartridge. In other words, to achieve correct and save function, it is important that users of such pen injectors ensure that the cartridge holder is fully engaged with the device mechanism before doses are dispended.
As an example, reusable pen injectors are known in which the cartridge holder is attached to the drug delivery device mechanism by means of a helical thread or a bayonet. Further, it is known to provide visual features on the drug delivery device and/or on the cartridge holder to assist users in determining when the cartridge holder is fully engaged. Typically, such visual features are provided on the outer surfaces of both the cartridge holder and an outer housing of the drug delivery device that line-up with each other only if the cartridge holder is fully locked to the drug delivery device.
In addition to such visual alignment features, the outer surfaces of known cartridge holders are typically provided with a range of visual features. On one side there is usually a cartridge contents scale which is often printed or laser marked onto the cartridge holder. On other sides there may be an aperture or windows to permit viewing the cartridge components, a product name and a manufacturer's logo. In addition, detent features or a latch member for releasable engaging a cap of the drug delivery device may be provided on the cartridge holder. Thus, in some cases there might be a visual clutter on the external surface of a cartridge holder which may confuse the user.
WO 2010/037828 A1 discloses an assembly comprising a drug delivery device and a monitoring device adapted to detect an action taking place in the drug delivery device. The drug delivery device comprises a main portion with coupling means for a cover. The monitoring device comprises a housing portion, means for detecting an action taking place in the drug delivery device, and coupling means adapted to engage the coupling means on the main portion. By this arrangement the monitoring device can be placed in a pre-determined position relative to the main portion when the coupling means engage each other, thus allowing transmission of information between the monitoring device and the main portion. As the cover and the monitoring device use the same coupling means for attachment on the main portion, either the cover or the monitoring device may be attached at the same time. The coupling means, thus, has the single function of attaching on of said components.